Walsh began refereeing aged 16 and in a long career has ascended to the top of the game, refereeing matches at two Rugby World Cups and also the Super 14 final in 2007. However, the New Zealander's career has been blighted by several run-ins with the authorities. He was suspended for three days in 2003 following a row with England fitness coach Dave Reddin as Clive Woodward's side ended up with 16 men on the field during their pool clash with Samoa. And he was sidelined again in 2005, this time for four months, for verbally abusing British & Irish Lions wing Shane Horgan during the tour match against provincial side Taranaki. He refereed his first Test in 1998 and was also the first Television Match Official used in international rugby - fulfilling the role for New Zealand's clash with Tonga in 2000.

In 2009 he was stood down by the NZRU following an alcohol-related incident at a SANZAR conference, but was offered a two-year contract by the Australian Rugby Union and resumed his refereeing career first in the Shute Shield and eventually in Super Rugby. There was further controversy midway through the 2010 Super 14 season when Brumbies fly-half Matt Giteau publically criticised Walsh for his performance in their loss to the Waratahs. Walsh was replaced as referee for the Brumbies' next clash with the Reds, while Giteau was fined for his outburst, but the Kiwi returned to the rotation the following week. Walsh made a low-key return to the international stage with the Japan v Samoa Pacific Nations Cup match in June. Walsh will return to the biggest stage in November 2010 when he takes charge of Wales v South Africa at the Millenium Stadium.